Medium
48 on Viessmann Vitodens 300-W

Your boiler has lost communication with a temperature sensor in your secondary heating zone, causing that specific circuit to shut down as a safety precaution.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

Mixer closes: Heating circuit M2 flow temperature sensor lead break

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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